Preparation of stable sub 10 nm copper nanopowders redispersible in polar and non-polar solvents

• Sub 10 nm PVP–PEG protected copper nanoparticles have been prepared.
• Centrifugation and ethanol precipitation employed to prepare Cu nanopowder.
• Cu nanopowder was redispersed in water, DMF, DMSO, chloroform.
• Concentrated Cu colloid has been successfully phase transferred.
• Toluene soluble Cu nanopowders have been successfully produced.

In this work we prepare 10 nm copper nanopowders redispersible in various polar and non-polar solvents. First, concentrated colloid of copper nanoparticles protected by PVP–PEG is synthesized by a simple wet chemical method using hydrazine hydrate as reducing agent. Extremely stable copper nano-powder containing sub 10 nm particles can be readily prepared by drying this colloid. This powder readily disperses in water, DMF, DMSO and choloroform and produces a stable colloid. To increase the copper content of the powder, washing of the colloid using (i) high speed centrifugation and (ii) ethanol addition and centrifugation at lower speed have been successfully conducted. The high speed centrifugation increases the size of the colloid to 50 nm after re-suspension while the size remains sub-10 nm when washing is conducted using ethanol. Particles were also phase transferred successfully from the aqueous polymeric solution to toluene using a protocol previously used for gold nano-rods. Many other simpler phase transfer techniques have also been tried but such methods failed to transfer particles from such polymer loaded colloid efficiently. Stable organic dispersible nanopowders have been produced from the organosol. The particle size is preserved after phase transfer and redispersion in organic solvent.

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